Hundreds of convicts, including senior members of al Qaeda, broke out of Iraq’s Abu Ghraib jail as comrades launched a military-style assault to free them, authorities said on Monday.

The deadly raid on the high-security jail happened as Sunni Muslim militants are gaining momentum in their insurgency against the Shi’ite-led government that came to power after the U.S. invasion to oust Saddam Hussein.

Suicide bombers drove cars packed with explosives to the gates of the prison on the outskirts of Baghdad on Sunday night and blasted their way into the compound, while gunmen attacked guards with mortars and rocket-propelled grenades.

Other militants took up positions near the main road, fighting off security reinforcements sent from Baghdad as several militants wearing suicide vests entered the prison on foot to help free the inmates.

Ten policemen and four militants were killed in the ensuing clashes, which continued until Monday morning, when military helicopters arrived, helping to regain control.

By that time, hundreds of inmates had succeeded in fleeing Abu Ghraib, the prison made notorious a decade ago by photographs showing abuse of prisoners by U.S. soldiers.

“The number of escaped inmates has reached 500, most of them were convicted senior members of al Qaeda and had received death sentences,” Hakim Al-Zamili, a senior member of the security and defense committee in parliament, told Reuters.

“The security forces arrested some of them, but the rest are still free.”

One security official told Reuters on condition of anonymity: “It’s obviously a terrorist attack carried out by al Qaeda to free convicted terrorists with al Qaeda.”